Electronic controller for predetermined temperature coefficient heater

ABSTRACT

An electronic controller for a predetermined temperature coefficient heater provides solid state control of the application of power to the heater. In particular, a positive temperature coefficient glow plug wherein the heater is plated on a ceramic substrate glow plug is controlled by contactless solid state controller. The temperature of the glow plug is sampled by a clock signal and compared with a predetermined temperature value. Pulsed power is supplied to elevate and maintain the temperature of the heater to the predetermined value. In a complete motor vehicle engine wherein one glow plug is used in each cylinder, one glow plug is sampled and controls the remainder of the plugs.

This invention relates to controllers for predetermined temperaturecoefficient heaters in general, and more particularly to a solid-statecontactless controller for wireless glow plugs for diesel engines.

CROSS-REFERENCE TO RELATED APPLICATIONS

U.S. Pat. No. 4,607,153, issued on Aug. 19, 1986, entitled "ADAPTIVEGLOW PLUG CONTROLLER" and filed by Leoncoi T. Ang on Feb. 15, 1985, andassigned to a common assignee."

BACKGROUND OF THE INVENTION

Compression ignition engines or diesel engines rely on the pressure andresultant temperature of the fuel in the cylinder in order to causeignition to drive the engine. As is well known, in each cylinder it isnecessary to provide a glow plug to raise the temperature of the fuelduring cold starts and other conditions when the fuel and environmentaltemperatures are low. Glow plugs are typically wire wound devices havinga very low resistance. These devices are electrically connected througha controller across vehicle batteries drawing heavy current loads. Thereason for the low resistance is to generate a high temperature in ashort response time.

Controllers for wire wound glow plugs contain one or more relays and oneor more relay contacts in the circuit in order to open and close thepower path to the glow plug. This opening and closing operates toregulate the amount of current flowing to the glow plug as well asturning the glow plug off when the temperature of the engine issufficient for compression ignition.

Wire wound glow plugs are now being replaced with solid-state glow plugswherein a predetermined temperature coefficient heating material, suchas a positive temperature coefficient material is deposited on a ceramicbase. This glow plug is then positioned in the cylinder in a mannersimilar to its wire wound predecessor. The resistance value of theheating material on the glow plug is generally higher than that of thewire wound on the glow plug, however, the heating time of the positivetemperature coefficient material is much faster than the wire wound. Inorder to accurately control the heating of the solid state glow plugs,it is necessary to replace the relays and the several contacts withfaster acting solid state components.

SUMMARY OF THE INVENTION

In order to solve the above-identified problem there is disclosed hereinan electronic controller for heating a device having a predeterminedtemperature coefficient heating material deposited on a ceramic base. Inparticular, such a device may be a glow plug for a diesel engine orgenerally may be any type of electrical heating device. In thecontroller there is a means responsive to the flow of current throughthe heating material to generate an electrical signal proportional tothe resistance of the material. Additioally, there is a means generatinga signal representing a predetermined resistance value of the material.These two signals are brought together to generate a signal of one levelwhen the electrical signal proportional to the resistance of thematerial indicates that its resistance is less than the predeterminedresistance. In addition, another signal of another level is generatedwhen the predetermined resistance is less than the resistance of thematerial.

The above-described controller can be used in an overall system forcontrolling positive temperature coefficient glow plugs for startingdiesel engines by locating at least one glow plug in each cylinder ofthe diesel engine. A power supply is provided for supplying power toeach of the glow plugs under the control of the controller. One of theglow plugs is sensed to generate a first electrical signal proportionalto the temperature of the glow plug. Another means is provided fordetermining the operating temperature of the engine and to generate asecond electrical signal proportional to the actual operatingtemperature. A fourth electrical signal is generated representing apredetermined operating temperature of the engine. The output of theelectronic controller is then supplied to a means which is responsive tothe two temperature signals for controlling the supplying of the powerto the glow plugs when the actual temperature is less than thepredetermined operating temperature.

It is, therefore, a principle advantage of the invention to provide acontactless controller for controlling predetermined temperaturecoefficient glow plugs.

It is another advantage of the system to provide a controller sensingone of a plurality of glow plugs and for controlling the operation ofall the glow plugs in response thereto.

These and other advantages will become apparent from the followingdrawings and detailed description.

DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a block diagram of one embodiment of an electronic glow plugcontroller.

FIG. 2 is a schematic of the embodiment of FIG. 1.

FIGS. 3A, 3B and 3C are graphic illustrations of the voltage and currentat different points in FIG. 2.

FIG. 4 is a block diagram of the system using the glow plug controller.

DETAILED DESCRIPTION

Fast-acting glow plugs of the type found in U.S. Pat. No. 4,545,339,issued Oct. 8, 1985, and entitled "Glow Plug Having a Conductive FilmHeater" by Mark A. Brooks et al, provide a fast-acting temperaturedevice to cause ignition in a diesel engine during times such as coldstart. An improved version of the above-identified glow plug is found inU.S. patent application No. 507,254, filed on June 23, 1983 and entitled"An Improved Glow Plug Having a Resistive Surface Film Heater" by MarkA. Brooks et al. Both of the above are assigned to the same assignee asthe present invention and incorporated herein by reference.

Referring to FIG. 1, there is illustrated in block form an electroniccontroller according to the present invention that is applicable for theabove-identified glow plugs. FIG. 1 neither shows, illustrates, norrequires devices such as relays or contacts to control the power withinthe controller. It is well known that if this is used in an automobileor other motor vehicle, the power from the battery is switched powerunder control of an ignition key or similar device but in the system ofFIG. 1, the power controlled by the controller is not switched throughcontacts. The controller may be described as a single channel controllerinasmuch as it controls one glow plug. Since most diesel engines havemore than one cylinder, the circuit of FIG. 1 may be duplicated an equalnumber of times as there are number of glow plugs in the engine.However, as will be shown hereinafter, sophistication in the form oftime sharing or multiplexing of the above circuit will provide forcontrolling more than one glow plug. In addition, additional glow plugscan be electrically connected in parallel.

Referring to FIG. 1, there is illustrated a clock means 10, sensingmeans 12 including a constant voltage source means 14 and a sensingresistor R1, a comparison means 16, a latch means 18, power switch means20, a glow plug 22 and a temperature reference means 24. The logic rulesfor this particular circuit require positive voltage levels for ON oractivating conditions and use positive going signals to actuate.

The clock means as used in FIG. 1 generates a pulse train having asample period and an activation period. In the preferred embodiment, thesample period is 200 microseconds and the overall clock period is sevenmilliseconds. This timing is a matter of design although the sampleperiod should be as short as possible. In the present method of sensing,it was found that the sensing resistor or R1 sensor was stable within200 microseconds after the application of sensing current. Therefore,this defined the sample period. Again, in the preferred embodiment thepulse train of clock signals comprises a negative going sample periodfor 200 microseconds after which time there is a positive going pulsewhich remains on for the remainder of the seven millisecond period.

The sensing means 12 as illustrated in FIG. 1 is responsive to thesample period signal from the clock 10 which through an inverter 26 is apositive going signal for turning on a constant voltage means 14. Theconstant voltage means 14 supplies a current equal to the voltage outputof the constant voltage means 14 divided by the summation of theresistance of the glow plug 22 and the sensing resistor R1. By measuringthe voltage drop across the glow plug 22 its resistance is determined.The temperature of the glow plug 22 is proportional to its resistance,thus the sensing means 12 in effect measures the temperature of the glowplug 22 and generates a temperature signal representing thattemperature.

The comparison means 16 receives the temperature signal from the glowplug 22 and a predetermined temperature reference signal from thetemperature reference means 24 and generates a comparison signalindicating the relationship of the predetermined temperature and thetemperature of the glow plug 22. The predetermined temperature referencemeans 24 generates an electrical signal having a characteristic which isidentical to the characteristic of the glow plug when it obtains itsoperating temperature. In the preferred embodiment as illustrated inFIG. 1, the temperature signal generated by the sensing means 12 and thepredetermined temperature reference signal from the temperaturereference means 24 are voltage signals and the output of the comparator16 is the signal of one polarity when the glow plug 22 is not at itsoperating temperature and a signal of another polarity when the glowplug 22 is at its operating temperature.

The latch circuit means 18 is activated during the activation periodfrom the clock means 10 and for storing the comparison signal togenerate a power applying control signal. The output of the latchcircuit means 18 is supplied to a logic means or logic gate 28 whichfunctions to insure that the power switch means 20 is off during thesample period. When both signals to the logic gate 28 are positive or atone voltage level, the output of the gate 28 is sufficient to activatethe power switch means 20. When the glow plug 22 is at temperature, theoutput of the comparator means 16 resets the latch circuit means 18,therefore, the latch signal and the clock signal being of oppositevoltage levels, causes the output of the logic gate 28 to turn off thepower switch means 20.

Referring to FIG. 2, the sensing means 12 comprises the circuit havingtransistor Q1 and Q2 which together are the constant voltage sourcemeans 12 supplying a constant voltage to the sensing resistor R1. Asillustrated, the collector lead of the resistor Q1 is connected througha resistor R6 to a regulated voltage from the regulated power supply 30and the emitter lead is grounded. The base lead is connected through anappropriate resistor R5 to the clock means 10. The collector oftransistor Q1 is also directly connected to the base of transistor Q2which is a Darlington amplifier connected in an emitter/followerconfiguration. The sensing resistor R1 is connected between the emitterof the Darlington amplifier Q2 and the glow plug 22. In the operation ofthe circuit under the control of the clock 10, the sensing resistor R1is responsive to the current flowing through the glow plug 22. Since theDarlington amplifier Q2 is a constant voltage source, the voltage at thejunction of the sensing resistor R1 and the glow plug 22 is a functionof the resistance of the glow plug 22; hence, the temperature of theglow plug 22.

The temperature reference means 24 illustrated in FIG. 2 is a voltagedivider means electrically connected in a bridge circuit with the glowplug 22 and sensing resistor R1. As illustrated, the voltage divider isa pair of resistors R12, R13 wherein the voltage signal at the junctionof the resistors R12, R13 with reference to ground is proportional tothe voltage across the glow plug 22 when the glow plug is at itsoperating temperature. The signal is connected to the inverting input 32of an operational amplifier IC2 in the comparison means 16. Electricallyconnected through resistor R3 to the noninverting input 34 of theoperational amplifier IC2 is the signal from the junction of the sensingresistor R1 and the glow plug 22. The output of the comparison means 16is connected to a conventional latch means IC3 having as another inputthe clock means 10. The output of the latch means IC3 is connected tothe logic means 28.

The logic means 28 comprises a pair of parallel transistors Q3 and Q4which are configured in a wired configuration. Transistor Q3 responds tothe clock signal and transistor Q4 responds to the signal from the latchmeans 18. The output of the logic means 28 is taken from the collectorsof Q3 and Q4 which are directly connected to the base of a secondDarlington amplifier Q5 in the power switch means 20. If the voltage atthe collector of either transistor is low, then the base voltage of thesecond Darlington amplifier Q5 is low and the Darlington amplifier Q5 isoff. However, if the voltage at both collectors is high, the transistorsQ3 and Q4 being out of conduction, the base voltage of the secondDarlington amplifier Q5 is high and it is turned on. Turning on thesecond Darlington amplifier Q5 turns on the power transistor Q6 allowingheavy current to be supplied to the glow plug 22.

FIG. 3A shows the current flow through the glow plug 22 duringconsecutive clock periods when the glow plug 22 is on. FIG. 3B shows thevoltage across the glow plug 22 as supplied through the power transistorQ6. FIG. 3C illustrates a graph of the resistance characteristic of theglow plug 22. As indicated, the glow plug 22 has a positive temperaturecoefficient and as such as the temperature of the glow plug rises, itsresistance also rises.

As illustrated in FIGS. 3A, 3B, and 3C there is a time period 36 whenthe resistance of the glow plug 22 is such that its temperature hasreached a predetermined operating condition. In the present embodiment,this condition is 1000° C. The temperature reference means 24 outputvoltage signal represents the expected voltage across the glow plug 22at 1000° C. This temperature is, of course, a matter of design. As shownin FIGS. 3A and 3B, when the output of the comparison means 16 indicatesthat the resistance of the glow plug 22 is at a value indicating a hightemperature, the power transistor Q6 is not turned on and the voltageacross the glow plug 22 is zero during the activation period of theclock. The time period 36 of FIGS. 3A and 3B illustrate that during thesampling period of the clock there is a small current through the glowplug 22 as well as a voltage across the glow plug 22.

While there has been discussed the application of the electroniccontroller to a positive temperature coefficient glow plug 22 as beingthe preferred embodiment, it is contemplated herein that this controlleris applicable to any predetermined temperature coefficient heatingdevice which transduces electrical power into heat. In such a device itrequires a sensing means 12 for sensing the temperature of the heaterand as a result of sensing the temperature, a temperature signal isgenerated representing that temperature. Depending upon the resistancevalue of the heating means and the desired level of heat to begenerated, this signal may represent temperatures below 100° C. as wellas temperatures well above 100° C. This temperature signal is thencompared with a predetermined temperature signal for generating acomparison signal having an output signal indicating whether the heateris above, below or equal to the predetermined temperature value. Theoutput of this comparison means is then supplied to a power drivercircuit which controls the application of power; namely, electricalcurrent to the heater.

All of the elements in the above controller are electronic in that thereare no contacts or relays necessary. The advantage of using a positivetemperature coefficient resistive material in the heating element isthat as the device reaches its operating temperature, the peak powernecessary to maintain the device at the operating temperature isreduced. The necessary power to operate the device is a function of thethermal mass of the device and its operating environment. If a negativetemperature coefficient heater was used, then as the temperature of theheater increased, the resistance would decrease and the amount ofcurrent supplied to the device would increase.

Thus, the method for controlling the heating of a predeterminedtemperature coefficient heater comprises the steps of sensing the amountof current to the hearter or in the alternative the voltage across theheater. This voltage or current is then compared to a predeterminedvalue of current or voltage which predetermined value represents thedesired heating temperature. Then as a result of the comparing of thetwo values, the amount of power supplied to the heater is modified so asto bring the value of the operating temperature of the heater to thedesired temperature.

Referring to FIG. 4, the above-described controller can be used in anoverall system for controlling positive or negative temperaturecoefficient glow plugs 22 for starting diesel engines by locating atleast one glow plug in each cylinder of the engine. A power switch 20 isprovided for supplying power to each of the glow plugs 22 under thecontrol of the controller, which is represented by the sensing means 16and the power switch 20. One of the glow plugs 22 is sensed to generatea first electrical signal V₁ proportional to the temperature of the glowplug 22. An engine temperature sensor 38 is provided for determining theoperating temperature of the engine and to generate a second electricalsignal V₂ proportional to the actual operating temperature. A thirdelectrical signal V₃ is generated from the glow plug temperaturereference means 24 representing a predetermined operating temperature ofthe glow plug 22. A fourth electrical signal V₄ is generated from anengine temperature reference means 40 representing a predeterminedoperating temperature of the engine.

The first and third electrical signals V₁ and V₃ are then compared 48and the resulting signal will be a representation of the relativetemperatures of the glow plug 22 and the glow plug temperature referencemeans 24. If the resulting signal indicates that the actual temperatureof the glow plug 22 is below the reference, this signal will be anactuating signal. In a similar manner the actual engine temperaturesignal V₂ and the engine temperature reference signal V₄ are compared 50and the resulting signal will be an actuating signal when the engine isbelow the reference temperature. An actuating signal is a signal which,by itself, will enable the controller to supply power to the glow plug.The outputs from the comparators 48 and 50 are then coupled through alogic means 52 to the electronic controller for controlling thesupplying of the power to the glow plugs 22.

Most systems may additionally include an ambient temperature sensor 44to determine the environmental temperatures of the system. This sensor44 generates an electrical signal V₅ which is supplied to a comparator54 with another electrical signal V₆ from an ambient temperaturereference means 46. The output of the comparison will be a signal whichwill be supplied to the logic means 52 indicating when the ambienttemperature is high to block operation of the controller.

The time when the power is to be applied to the glow plugs may also bedetermined. Such a time is generally on engine start-up or during a coldstart condition. The fuel being supplied to the cylinder is below thetemperature that is necessary for the fuel to be ignited in thecylinder.

Depending upon the configuration, there may be one controller per glowplug 22 or several glow plugs may operate from one controller asillustrated in FIG. 4. There the current is measured to the one glowplug that is selected to the measured glow plug. As a result of thismeasurement, the time base signal is generated for controlling theapplication of power to the remaining glow plugs. As previouslyillustrated, this time base signal may have a characteristic of eitherbeing on or off for one unit of time or such signal may be used tomaintain current to the glow plug until such time as the glow plugreaches tempeature.

There are other conditions which a system may respond to for controllingthe operation of the glow plug. One such condition may be a constraintas to the maximum time that the glow plug may be energized. Thus thecontroller may be used in an overall system wherein several conditionsare sensed. These conditions will be electrically coupled to thecontroller for controlling, as an end result, the application of powerto the glow plugs. As stated previously, time sharing, multiplexing andlarge capacity electronic components may be used to permit onecontroller to control all of the glow plugs in an engine.

What is claimed is:
 1. In a diesel engine a system for controllingpositive temperature coefficient glow plugs comprising:at least onepositive temperature coefficient glow plug in each cylinder of a dieselengine; clock means for generating clock signals having a sample periodand an activation period; contactless means for applying activatingcurrent to each of said glow plugs; means for sensing an amount ofsensing current to only one of said glow plugs during said sample periodof said clock means and generating a first electrical signalproportional to the amount of sensed current, said sensing current beingless than said activating current and said sensing means not responsiveto said activating current to said glow plugs; means for generating asecond electrical signal proportional to the actual temperature of thediesel engine; means for generating a third electrical signalrepresenting a predetermined glow plug temperature; means for generatinga fourth electrical signal representing a predetermined operatingtemperature of said engine; means responsive to said first and thirdelectrical signals during said activation period of said clock means foractivating said contactless means for applying activating current toeach of said glow plugs when said actual temperature is less than saidpredetermined operating temperature; and means responsive to said secondand fourth electrical signals for inhibiting said contactless means forapplying activating current to each of said glow plugs when saidtemperature of said engine is equal to said predetermined operatingtemperature.
 2. A contactless electronic controller for heating a singleglow plug comprising:a glow plug; clock means for generating clocksignals having a sample period and an activation period; a constantvoltage means activated by said sample period of said clock means; asensing resistor electrically connected in series between said constantvoltage means and said glow plug, said resistor responsive to thevoltage drop across said glow plug due to a sensing current flowingtherethrough for generating a voltage signal representing thetemperature of said glow plug; means for generating a voltage signalrepresenting the desired operating temperature of said glow plug;comparison means responsive to said voltage signals representing thedesired operating temperature and said temperature of said glow plug forgenerating a comparison signal when the temperature of said glow plug isless than the desired operating temperature; latch circuit meansresponsive to said activation period and said comparison signal forgenerating a power applying control signal; and contactless power drivercircuit means electrically connected series with said glow plug and inelectrical parallel with said constant voltage means and said sensingresistor and responsive to said power applying signal for supplyingactivating current to said glow plug for raising its temperature to thedesired operating temperature.